1. Field of the Invention
The present invention relates to an optical packet switching apparatus that switches the path of an optical packet transmitted thereto to the destination of the optical packet and transmits the optical packet and an optical switch control method that controls the ON/OFF states of an optical switch included in the optical packet switching apparatus.
2. Description of the Related Art
For avoiding the bottlenecks (limits in band and amount of signal) of electric wiring technologies in signal switching within a high-speed router, the application of an optical packet switch using a wide band characteristic of an optical transmission technology has been studied and has been partially implemented until now. An optical signal is once converted to an electric signal for switching in an optical packet switching system having been adopted until now, and the scale of the switching has been largely extended with the increase in bands. In order to avoid the large extension of the scale of switching, an optical packet switching apparatus has been considered that transmits an input optical packet by switching it with the optical signal as it is, without converting to an electric signal.
FIG. 1 is a diagram showing an example of a conventionally devised optical packet switching apparatus.
An optical packet 20 input to an optical packet switching apparatus 10A through an optical transmission line 31 on the input side is demultiplexed by an optical filter 12 into a header 21 including destination information and data information (payload 22) that is the body of the optical packet 20. The header 21 and payload 22 of the optical packet 20 have different optical wavelengths from each other, and the optical filter 12 uses the difference in wavelength to demultiplex the optical packet into the header 21 and the payload 22.
The header 21 of the optical packet 20 is converted to an electric signal by a photodetector 13 and is input to a switch control signal generating section 14. In the switch control signal generating section 14, switch control signals for switching the ON/OFF states of multiple optical switches provided in an optical switch section 16 are generated in accordance with the destination information in the header 21 and are input to the optical switch section 16.
On the other hand, the payload 22 demultiplexed by the optical filter 12 is input to the optical switch section 16 through an optical coupler 15.
Rendering in FIG. 1 as if there is one input port for simple illustration, multiple input ports and multiple output ports exist in reality (FIG. 3 shows an example having two input ports and two output ports).
The optical packet (payload 22) through the optical coupler 15 is input to the optical switch section 16. Multiple optical switches are provided in the optical switch section 16 for switching the path of an input optical packet. The optical switches are switched between the ON and OFF states in accordance with the switch control signals generated by the switch control signal generating section 14. The optical packet input to the optical switch section 16 passes through the path formed by the optical switch at the ON state among the optical switches, which are switched between the ON and OFF states in accordance with the switch switching signals generated based on the destination of the optical packet in the switch control signal generating section 14, and is output from an optical transmission line 32 on the output side.
FIG. 1 shows three optical packets #1 to #3, which are sequentially input, and schematically illustrates that the switch control signal is turned on, off and on and that the optical packets #1 and #3 are output from the output side while the optical packet #2 is blocked by the optical switch section 16.
Notably, showing in FIG. 1 (and other figures, which will be described later) as if the payload 22 of the optical packet 20 is only output to the optical transmission line 32 on the output side, a new header is added thereto and transmitted in reality by a configuration not shown herein.
When a skew occurs among multiple switch control signals having arrived at the multiple optical switches, a waiting time occurs among the packets, which causes the deterioration of the transfer efficiency, since no proper buffer element (delay element) exist that can hold an optical signal for a while as it is in a case where switching is performed with the optical signal as it is.
Japanese Laid-open Patent Publication No. 2001-53684 discloses a technology that controls the drift of an optical signal, but the technology cannot suppress the skew among switch control signals.